Pretty easy.

1) Soak the bleed valve in some sort of solvent (WD-40 or PBlaster) overnight or over weekend (I've often had these things break off and then you are up a creek)

2) Start the car up (so the booster is working) and press the brakes firmly while at a rest.

3) Jack up the offending wheel and confirm that the brake is indeed still dragging (hard/impossible to turn wheel).

4) Discern between lines/mastercylinder/whatnot and caliper by briefly opening the bleed valve (actually - there's two per caliper on a 140). If a little squirt of fluid comes out followed by the wheel unlocking then something is holding pressure on the caliper (swollen flexible lines, crimped/smashed hard line, something amiss with the master cylinder). If the caliper remains just as tight after doing both bleed valves (you can do them one at a time - just open for 1/2 second then snug shut again) then the caliper is the problem.

There no way to revive a sticky caliper in any meaningful way. Rebuilt replacements are the way to go.